Considerable interest exists in improving the efficiency of power plants which use gas turbines. In simple cycle gas turbines, the heat in the exhaust gases from the turbines is wasted, leading to a low overall cycle efficiency.
Regeneration (preheating the fuel) is a simple method of increasing the efficiency of a power plant; however, the increased efficiency comes at the cost of reduced power output of the system. The reduced power output, combined with the added expense of the preheating equipment, increases the fixed cost of operating a power plant and, ultimately, the cost to the consumer.
Some in the field recover some of the waste heat in the exhaust of a gas turbine. For example, a condensing steam turbine driven by steam generated with heat from the combustion gases of the gas turbine has been used. Closed circuit (combined cycle) approaches of this kind improve the efficiency of the plant considerably but are expensive because of the requirements for a condenser and a cooling water loop for the steam turbine, which may require cooling towers.
Other methods of recovering the heat from the exhaust gases use Chemically Recuperated Gas Turbines ("CRGT"). In the CRGT cycle, the waste heat from the gas turbine is recovered in chemical reformers. The CRGT cycle has advantages over a steam-injected gas turbine ("STIG") cycle, and gas turbines without steam injection, in reduced emissions of nitrogen oxides. With the use of natural gas, temperatures of 700-900.degree. C. are needed for reforming, whereas for alcohols, chemical recovery of the waste heat can be performed at lower temperatures with existing gas turbine technologies and recovery devices. Methanol, in particular, is particularly desirable due both to its intrinsic characteristics as a fuel (excellent combustion properties, low environmental pollution emissions, low reforming temperature) and to the possibility of being produced from any fossil fuel and any renewable organic matter.
There is a need for a power plant, with a simple turbine design and with increased efficiency and low capital costs, that does not sacrifice the total power output of the plant. The plant should preferably operate at relatively low temperatures and use a readily available fuel, such as methanol. The present invention satisfies this need.